# Motion of a charge

1. Feb 27, 2010

### thereddevils

Helium ion , He (2+) travelling at 1.0 x 10^5 m/s pass through a region where there is a uniform electric field of 2 x 10^4 V/m perpendicular to their initial path and extending for 0.10 m . Through what angle are they deflected ? [Charge of the electron , e=-1.6 x 10^(-19)C , mass of helium ion , m=6.7 x 10^(-27)kg]

well , this is what i did :

Resolve the velocity into 2 components , Vx and Vy where

Vx=1.0 x 10^5

ma=qE

a=(qE)/m

After doing some substitution , i found a to be 9.56 x 10^11

Vy^2=u^2+2as

Vy^2=2(9.56 x 10^11 )(0.10)

Vy=4.4 x 10^5

so the angle = tan^(-1) Vy/Vx

= 77 degree

but the given is about 84 degree ..

2. Feb 27, 2010

### rl.bhat

Hi thereddevils, welcome to PF.
The electric field is extended 0.10 m horizontally, not vertically.
Find time t required to cross this region by the helium ion.
In this time interval find Vy.

3. Feb 27, 2010

### thereddevils

thank you , bhat !

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